1. Field of the Invention
The present invention relates to polyurethane solutions having amino-functional heterocyclic stoppers, a process for preparing these polyurethane solutions and the use of the corresponding polyurethane solutions.
2. Description of the Prior Art
Polyurethane solutions are known and are described, e.g., in D. Diederich, Methoden der Organischen Chemie (Houben-Weyl), vol. E20, Georg Thieme Verlag, 1997 and literature cited therein.
Polyurethane solutions are generally high molecular weight reaction products of aliphatic and/or aromatic di- or polyisocyanates with di- or tri-functional polyols and/or diamines. Reaction of the isocyanate compounds with the hydroxyl and/or amino-functional compounds takes place at an equivalent ratio of approximately 1:1 to produce the required high molecular weight.
In order to obtain soluble and readily processable products, the chain building reaction has to be terminated when the desired molecular weight or desired viscosity the polyurethane solutions is achieved. This generally takes place by adding low molecular weight, reactive compounds, such as a monoamine (DE-A-2,633,293), a monoisocyanate or acetanhydride (DE-A-2,500,921, EP-A-0,129,396), a monofunctional alcohol, e.g., methanol, or by adding other chain terminating compounds, e.g., butanonoxime (DE-A-3,142,706).
When practiced on an industrial scale an excess of chain terminator is generally added to ensure reliable stopping of the reaction. This excess, however, may also have a deleterious effect on the properties of the coatings, which may then become manifest in the form of odors, exudation or adhesion problems or by defects in the film due to the formation of bubbles or craters. Also, the storage stability of polyurethane solutions may be impaired. Excess free monoamine, monoisocyanate or reactive monoalcohol may lead to considerable viscosity changes or to serious degradation (associated with an impairment in the properties due to a slow reaction with the urethane or ester bonds in the polymer), especially during storage.
Since polymer solutions generally no longer contain reactive groups, only a physical drying process takes place after application. Chemical linking via reactive groups at the ends of chains with reactive groups in the substrate is not possible.
DE-A-3,401,753 discloses polyurethane solutions with terminal amino groups which are available for subsequent cross-linking reactions. However, these require the subsequent addition of a reaction partner.
An object of the present invention is to provide polyurethane solutions which do not have the disadvantages mentioned above, in particular, to provide polyurethane solutions which contain polyurethanes having a high molecular weight, which can be prepared and stopped reliably and which do not cause any problems due to inadequate adhesion or inadequate optical film properties when used in coatings. Thus, it has to be ensured that any excess amounts of stopper which are added do not impair the storage stability of the solution and do not impair the properties of the coating.
Surprisingly, it has now been found that polyurethane solutions which incorporate amino-functional heterocyclic compounds as stoppers satisfy these requirements. Coatings based on the polyurethane solutions according to the invention have good adhesive properties and a particularly pleasant feel. It was also found that the polyurethane solutions according to the invention are extremely suitable for preparing high quality coatings with high permeability to water vapor and thus exhibit an associated outstanding wearer comfort. The coatings according to the invention, therefore, combine high permeability to water vapor with very good water resistance or waterproof character and a relatively low degree of swelling in water.